1. Field of the Invention
The present invention relates to a device for damping oscillation of a crankshaft and including a hub fixedly mountable on the crankshaft, a flywheel connected to the hub, and a torque-transmitting element, in particular, a belt pulley.
2. Description of the Prior Art
Damping devices of the type described above are primarily used for quenching or damping of high frequency crankshaft oscillations. Auxiliary apparatuses, which are driven by an internal combustion engine, such as generators, cooling water pumps, as a rule, are driven by V-belts or so-called multi-V-shaped belts. The auxiliary apparatuses are driven either by the oscillation dampers (the belt track forms a component of an oscillation damper), or by separate belt pulleys, or by belt pulleys with a torsionally elastic coupling. The torsionally elastic coupling serves for isolating the belt drive from oscillations resulting from large amplitudes of the crankshaft rotational angle observed in the region of small rotational speeds of an internal combustion engine (which are associated with functional rotational irregularities of piston engines). To this end, the spring characteristic of the coupling should be made so flexible that a torsional oscillation system, which is formed by the coupling and the auxiliary apparatus, has a very low first fundamental frequency. For engines and small diesel engines, these torsional oscillation dampers are formed usually as elastically suspended dampers in which both elastic and damping characteristics are provided by a rubber spring. This rubber damper is formed primarily of a hub connectable with a crankshaft, one or two rubber springs and one or two balance weights. The rubber springs can be provided in a bound form (be vulcanized or bonded) and a non-bound form (be pressed on), or be glued. The functioning of the rubber damper is based on a combination of quenching and damping.
However the power of these rubber dampers is not sufficient, e.g., for large Diesel engines. With these engines, co-called viscous dampers are used. The viscous dampers are based on a physical principle of shear flow of liquid in an annular clearance between a balance weight and a housing which is connected with the crankshaft and in which the balance weight is arranged. The freely rotatable balance weight, as a result of its rotational inertia, slows down the movement of the housing. With that, the energy necessary for shearing the viscous fluid in the clearance is reduced and, therefore, the oscillations are damped.
A device of this type is disclosed in German publication DE-43 28-596A1. This publication describes a torsional damper formed as a rubber damper connected seriesly with or parallel to a viscous coupling for decoupling of a belt drive of an auxiliary apparatus. This coupling has a backlash, and the damper includes a rubber spring. Because of a noticeable difference of rotational speeds between the belt pulley and the crankshaft and because of the losses, which are caused by this difference, the device described in this German publication is not economical and, moreover, could hardly be realized from the thermal point of view.
Accordingly, an object of the present invention is a damping device capable of reducing high frequency torsional vibrations of a crankshaft and, at the same time, capable of isolating low frequency oscillation without significant losses.